Multi-walled Carbon Nanotubes Content Research Articles

COMPARING THE PERFORMANCE OF USING NANOFLUIDS IN TWO DIFFERENT TYPES OF HEAT EXCHANGERS WITH THE SAME HEAT TRANSFER AREA

Using multi-wall carbon nanotubes (MWCNTs) based on distilled water with varied volume concentrations, experimental research was conducted. The performance of two distinct heat exchangers with the same heat transfer area was assessed. A tubular heat exchanger (THE) and a shell-and-tube heat exchanger (STHE) with a heat transfer area of 20,000 mm<sup>2</sup> were employed. A tubular heat exchanger (HT31) and a shell-and-tube heat exchanger (HT33) are available from Armfield for use with the heat exchange service unit (HT30X). Three volume concentrations of nanomaterials are used to create nanofluids (0.5%, 1%, 2%). While the rate of flow was the same in the heat exchangers, the Reynolds number of the flow inside the tube ranged from 1600 to 7800 for THE and from 2500 to 12,500 for STHE due to different inside diameters. The measured variables determine the coefficient of heat transfer, friction factor, Nusselt number, and effectiveness. The heat transfer coefficient in both heat exchangers was boosted with increasing MWCNT content, according to the experimental data. Because of the nanoparticle concentration, the heat transfer coefficient of STHE is 7-43% greater than that of THE. With the increase of nanofluid concentration, the Nusselt numbers were enhanced for the two heat exchangers. The increase in the Nu number for THE is higher than in its value for STHE within a range of 28.5-40%. Correlations between the Reynolds number and MWCNT volume concentration are proposed for each heat exchanger to compute the Nusselt number and friction factor. The results of the current study have been compared with previous studies and acceptable agreement can be found.

In English

The mechanical mixtures of titanium oxide (TiO2) with carbon nanostructures for 3D printing of CJP technology, which are used as consumables for the manufacturing of electrically conductive composite 3D products, are created in this work. Various carbon nanostructures (single- and multi-walled carbon nanotubes and carbon nanofibers) were used in the creation of composite 3D products (TiO2–СNS) by CJP 3D printing technology. Optimal conditions for processing of mechanical mixtures (TiO2/MWCNT) on a planetary ball mixer for composite 3D products (CJP) were studied and proposed. The dose of the deformation influence on the mechanical mixture under optimal conditions of mechanochemical processing (76 J/g), which allows not to deteriorate the electrical conductivity of the material, is determined. The dependence of the electrical conductivity of composite 3D products (CNS/TiO2, where the CNS content is 3 wt. %) on the type of carbon nanostructures (SWCNT, MWCNT and CNF) contained in ceramics (TiO2), is constructed. The exponential dependence of the specific electrical conductivity (G) of composite 3D products (TiO2–MWCNT) on the mass content of multi-walled carbon nanotubes, is also recorded in the work. In the framework of the study of the electrical conductivity of composite 3D products (CJP), a fuel cell cathode based on a Pt/TiO2–MWCNT composite was created. It was found that the catalyst Pt/TiO2–MWCNT, which contains 5 wt. % of carbon nanotubes, has the best catalytic activity in oxygen recovery. At the same time, the average particle size of platinum (Pt) is 5–10 nm, while the content of Pt in the EDX samples is approximately ~10 wt. %. Also, studies were carried out from the mixing of Pt/TiO2-MWCNT composites with MWCNT content 15 and 50 wt. %. Samples were analyzed by transmission and scanning electron microscopy.

Bridge-graphene connecting polymer composite with a distinctive segregated structure for simultaneously improving electromagnetic interference shielding and flame-retardant properties

With the development of modern electronic technology, there is an urgent demand for the fabrication of multifunctional composites with electromagnetic interference (EMI) shielding and flame-retardant properties. Herein, a novel microcapsule structure is formulated by modifying the hydrophilicity of polypropylene (PP) micro-powder surface and wrapped with graphene oxide to modulate the distribution state of multi-walled carbon nanotubes (MWCNTs). The modified PP/reduced graphene oxide/MWCNTs (mPP/RGO/MWCNTs) composite with a distinctive segregated structure is obtained by hot-pressing of the microencapsulated PP micro-powder. The influence of the contents of MWCNTs and RGO on composite’s EMI shielding and flame-retardant properties are further investigated. Interestingly, the results show remarkable synergistic effect between MWCNTs and RGO, enhancing the electrical conductivity and EMI shielding property of the composites. Moreover, the segregated structure of mPP/RGO/MWCNTs composite enhances EMI shielding and flame-retardant properties compared with pure PP and mPP/MWCNTs. Therefore, this work provides new insights into the rational design of EMI shielding polymer composite with segregated structures to realize high EMI shielding performances and good flame-retardant properties.

Qualitative Assessment of MWCNT- Treated Grains of Some Food Cereals

Abstract: The advancement in nanotechnology and its utilisation in agriculture increases agricultural output. To protect crops from numerous plant diseases and pests, excessive chemical, pesticide, and fungicide use can be replaced with nanoparticles. The first step of plant growth, seed germination, is thought to be the most delicate time in a plant's life cycle. The effects of carbon nanotubes on seed quality and seed content both before and after treatment are discussed in this study. Rice, wheat, and oat grains were compared with the seeds harvested from MWCNT (multiwalled carbon nanotubes) treated plants at three different concentrations (70, 80, and 90μg/ml) and indicated no significant changes in various components such as carbohydrates, protein, crude fat, crude fibre, moisture and ash contents when compared to untreated grains. Grain primed with MWCNT before sowing resulted in no change in the above components, but an increase in mineral accumulation was found. Here, we noticed a significant increase in grain yield. The treatment of MWCNT enhanced the growth of grains count by two folds compared to the control plant. The wheat grain had a moisture content: 9.3-9.38%, ash content: 1.31-1.35%, crude fat: 0.9-0.93%, crude fibre: 1.1-1.13%, protein content: 9.2-9.38%, carbohydrate content: 77.96-78.04%. The rice grain had a moisture content: 9.98-10.25%, ash content: 0.42-0.45%, crude fat: 1.00-1.02%, crude fibre: 0.9-0.93%, protein content: 4.42-4.49%, carbohydrate content: 82.92-83.03%. The oat grain had a moisture content: 8.95-9.3%, ash content: 1.74-1.8%, crude fat: 2.1-2.3%, crude fibre: 5.1-5.27%, protein content: 9.5-9.59%, carbohydrate content: 71.78-72.23%. The study revealed that the examined MWCNT concentrations might efficiently enhance the grain yield without altering the grain quality.

Effect of Multi-Walled Carbon Nanotubes (MWCNTs) in Reducing the Corrosion Rate in Cr-MWCNTs Composite Coatings

Carbon steel was coated with Cr-multi-walled carbon nanotube (MWCNTs) coatings via electrodeposition. In this article, the impact of a combination of MWCNTs into the chromium coating on the morphology of the coating surface and corrosion characteristics was inspected. The MWCNTs seem to be evenly distributed across the chromium layer, according to scanning electron microscopy (SEM). Electrochemical measurements were used to conduct corrosion tests on samples of MWCNTs– chromium composite coated and pure chromium coated samples in aqueous NaCl (3.5 wt.%). The outcomes demonstrated a considerable increase in the resistance of corrosion due to the inclusion of MWCNTs during the chromium deposition procedure. In addition, the mechanism of anti-corrosion of the composite coating is also presented. Using an electrolyte bath containing various concentrations of dispersed MWCNTs (0.5, 1, and 1.5 g/L), crack-free and compact coating of Cr-MWCNT composite were electrodeposited on the substrates of the mild steel. The potentiodynamic polarization technique was used to examine the coatings corrosion performance subjected to a 3.5 weight percent of NaCl medium. When compared to chromium coating, the Cr-MWCNT composite coating showed the lowest corrosion rate (1.045x108 mpy) compared to chromium coating (4.891x108 mpy).

In vitro comparative cytotoxic assessment of pristine and carboxylic functionalized multiwalled carbon nanotubes on LN18 cells.

Multiwalled carbon nanotubes (MWCNTs) have been used in biomedical applications due to their ability to enter the cells. Carboxylic functionalization of MWCNT (MWCNT-COOH) is used to mitigate the toxicity of MWCNTs. Our study focuses on comparing the toxicity of MWCNT and MWCNT-COOH on the neuronal cells, LN18. Concentrations of 5, 10, 20, and 40 µg ml-1 were used for the study, and cytotoxicity was determined at 0, 1, 3, 6, 12, 24, and 48 h of incubation. Cell viability was assessed by Trypan Blue, MTT, and Live dead cell assays, and the oxidative stress produced was determined by reactive oxygen species (ROS) and Lipid peroxidation assays. MWCNT-COOH showed higher cell viability than MWCNT for 20 and 40 µg ml-1 at 24 and 48 h. This was also visually observed in the live dead cell imaging. However, at 48 h, the morphology of the cells appeared more stretched for all the concentrations of MWCNT and MWCNT-COOH in comparison to the control. A significant amount of ROS production can also be observed at the same concentration and time. Viability and oxidative stress results together revealed that MWCNT-COOH is less toxic when compared to MWCNT at longer incubation periods and higher concentrations. However, otherwise, the effect of both are comparable. A concentration of 5-10 µg ml-1 is ideal while using MWCNT and MWCNT-COOH as the toxicity is negligible. These findings can further be extended to various functionalizations of MWCNT for wider applications.

Mechanical, Thermal Stability and Water Absorption Properties of Recycled Thermoplastic Blend Nanocomposites: Comparison of Nanoclay and Carbon Nanotube

This present paper investigates the influenceof clay (Cloisite 10A) and multiwalled carbon nanotubes (MWCNT) loading for the tensile, flexural, thermal stability and water absorption properties of recycled thermoplastic blend made from recycled high-density polyethylene (rHDPE)and recycled polyethylene terephthalate (rPET). The nanocomposites were prepared via extrusion blending technique by using extruder and compressed using hot and cold press molding machine. The findings showed that the sample with 1 phr of Cloisite 10A and 4 phr of MWCNT showedthe optimumof tensile strength at 13.9 MPa and 14.5 MPa as compared to other loadings. The flexural strength exhibited inconsistent trend with the increasing of Cloisite 10A and MWCNT content. The addition of Cloisite 10A and MWCNT-reinforced nanocomposite showed better thermal stability than pure polymer blend. As the increment of Cloisite 10A and MWCNT loading, the percentages of water uptake increased but the values were still lower than the neat thermoplastic blend.

Nutrient removal from biogas slurry and biogas upgrading by microalgae-fungi-bacteria co-cultivation under different carbon nanotubes concentration.

In this study, Chlorella vulgaris, Ganoderma lucidum, and endophytic bacteria were co-cultivated with the stimulation of strigolactone analogs GR24 to prepare pellets. During the purification of biogas slurry and biogas, multi-walled carbon nanotubes (MWCNTs) were introduced to enhance the removal efficiencies of nutrients and CO2. The results showed that both GR24 and MWCNTs affected the purification of biogas slurry and biogas. The maximum chemical oxygen demand, total nitrogen, total phosphorus, and CO2 removal efficiencies of the Chlorella vulgaris-Ganoderma lucidum-endophytic bacterial symbionts were 82.57 ± 7.96% (P < 0.05), 82.14 ± 7.87% (P < 0.05), 84.27 ± 7.96% (P < 0.05), and 63.93 ± 6.22% (P < 0.05), respectively, with the induction of 10-9M GR24 and 1mg L-1 MWCNTs. Moreover, the growth and photosynthetic performance of the symbionts were consistent with the removal effects. The Chlorella vulgaris-Ganoderma lucidum-endophytic bacterial symbionts obtained high growth rates and enzyme activity with the maximum growth rate of 0.365 ± 0.03d-1, mean daily productivity of 0.182 ± 0.016g L-1 d-1, and carbonic anhydrase activity of 31.07 ± 2.75 units, respectively. These results indicated that an appropriate concentration of GR24 and MWCNTs could promote the growth of symbionts, reinforce the purification effects of biogas slurry and biogas, and provide a new idea for the simultaneous purification of wastewater and biogas.

Combination of enhanced strength-ductility trade-off and stress relaxation resistance of MWCNTs reinforced Sn–5Sb-0.3Cu matrix composite

In this study, the strength-ductility trade-off and stress relaxation (SR) behavior of Sn–5Sb-0.3Cu (SSC503) alloy reinforced with (0, 0.05and 0.1 wt%) multi-walled carbon nanotubes (MWCNT) have been investigated under different pre-strains and initial stress levels. The results show that the pre-deformation can extend the duration of initial SR stage and significantly promote the stress reduction rate. The SSC503–0.05MWCNT composite alloy exhibits the optimum increase in SR resistance, yield strength (σy), ductility, and creep threshold stresses with the values of 75.8%, 17.3%, 77.9% and 10.6%, respectively. The scanning transmission electron microscopy (STEM) images and electron probe microanalyzer (EPMA) revealed that the distribution of MWCNT in SSC503 alloy was concentration dependent. 0.05MWCNT concentration induced a dendritic/cellular transition of β-Sn grains and restrained the growth of β-Sn, Cu6Sn5, SnSb, Sn3Sb2 and Cu2Sb IMC compositions, whereas 0.1MWCNT led to the partial agglomeration of MWCNT into β-Sn grain surfaces. MWCNTs are adsorbed at the surface-active atoms of Sb metalloid to form Sb-coated MWCNTs (Sb/C) in situ, which act as a bridge between MWCNT and Cu6Sn5 particles. The modified composites represent a vital technological progress for utilization in high temperature solder applications.

Multi-scale integrated design and fabrication of ultra-broadband electromagnetic absorption utilizing multi-walled carbon nanotubes-based hierarchical metamaterial

Ultra-broadband electromagnetic absorption has become a critical issue competing with advanced broadband electromagnetic detection systems. In this study, an innovative strategy for the broadband absorption is proposed via combining periodic patterns and the hierarchical structure with gradient electromagnetic performance, which introduces an abnormal electromagnetic response for improved maneuverability in impedance matching and multiple electromagnetic loss mechanisms. The electromagnetic parameters for each layer were determined by the fixing content of multi-walled carbon nanotubes (MWCNTs) in gypsum, and the periodic stepped meta-structure was optimized via the finite element simulation. The optimized hierarchical MWCNTs/gypsum metamaterial with a thickness of 8.0 mm realized an average absorption intensity of −21.6 dB (>99.3% absorption) in the frequency band of 4–40 GHz. Particularly, broadband EM absorption for reflection loss less than −10 dB and −15 dB was achieved in the ranges of 4.2–40 GHz and 5.6–40 GHz, respectively. The ultra-broadband and strong electromagnetic absorption properties of the proposed metamaterial should be the synergic result of the excellent impedance matching and the multiple EM wave loss caused by the multi-scale integrated structure. Therefore, the proposed MWCNTs/gypsum metamaterial with the innovative strategy of combining the hierarchical structure and periodic patterns, could provide an insight for achieving high-performance absorption materials.

A novel carbon nanotubes doped natural rubber nanocomposite with balanced dynamic shear properties and energy dissipation for wave energy applications

Mechanical characterizations of natural rubber filled with carbon-based nanomaterials were extensively studied in tensile and tear modes whereas fewer attempts have been conducted on a dynamic shear condition using a double-bonded shear test piece. This is of importance since natural rubbers are widely used as flexible membranes for wave energy harvesting devices. Therefore, this study was aimed to explore the microstructural, rheological, and dynamic viscoelastic characteristics of natural rubbers filled with different Multi-Walled Carbon Nanotubes (MWCNTs) contents. A combined compounding approach was employed to ensure a homogenous CNT dispersion was achieved. Transmission electron microscopy (TEM) was performed for the materials characterization while the processability and curing parameters of the compounds were investigated using the Mooney viscosity and rheometry test. Dynamic shear properties were compared using a cyclic test performed on a double-bonded shear test piece. TEM images showed that an optimum CNTs dispersion was reached at 3 phr MWCNTs loading whereas increasing CNT content resulted in further inhomogeneity. The addition of CNTs into the natural rubber not only improved the curing properties of the compound, i.e., low scorch and curing times, but it also increased the Mooney viscosity, the rheological properties, and the dynamic shear properties of the nanocomposite compared to the pristine rubber. The Payne and Mullins effects were also observed for all compounds manifesting dependency on the CNTs content and applied strain amplitude. Finally, MWCNT enhanced the dissipated energy of the nanocomposites with respect to the neat rubber in which an increase of 1040 % in energy dissipation for 10 phr MWCNTs compared to the control at a strain amplitude of 200 % was achieved.

Development of nanomodified self-healing mortar and a U-Net model based on semantic segmentation for crack detection and evaluation

In this study, a cement-based self-healing (SH) mortar mixed with multiwalled carbon nanotubes (MWCNTs) was developed, and the effect of MWCNT addition on the electromechanical properties of mortar was studied. In addition, a deep learning based U-shaped Network (U-Net) model was adopted for the crack healing evaluation in SH mortar specimens. The trained U-net model is capable to detect the cracks with the accuracy of 99 %. The MWCNT content in the mortar was varied from 0.05 % to 0.10 % by weight of the cement. A minerals-based SH admixture was incorporated at concentrations of 2.5 %, 5 %, and 7.5 % by weight of cement. Compression and flexural strength tests were performed to investigate the mechanical performance of the nanomodified mortar. Piezoresistive sensing properties of MWCNT/cement composite were monitored during flexural test. For crack healing evaluation, cracked mortar prisms were exposed to water for 28 days. Mechanical and piezoresistive sensing evaluation demonstrated improved mechanical performance of SH mortar with appreciable self-sensing properties. Specimens with 2.5 % admixture exhibited a crack sealing efficiency of approximately 90 %, while the cracks in specimens with 5 % and 7.5 % SH admixture content healed 100 % after 28 days of water exposure.

Effect of multi-walled carbon nanotubes on durability of high-strength slag-based geopolymer

The effect of multi-walled carbon nanotubes (MWCNTs) on the durability of high-strength slag-based geopolymers was investigated. The control variables were the MWCNT content and MWCNT/dispersant and water-cement ratios. A total of 144 specimens were exposed to carbonization, freeze-thaw cycles, and chloride migration (RCM). The microstructure of the geopolymers before and after durability testing was observed using scanning electron microscopy (SEM). The modification of pore structure of geopolymer by MWCNTs was measured by mercury intrusion porosimetry (MIP). The composition of the materials was analyzed using X-ray diffraction (XRD), and the contents of the materials were determined quantitatively using thermal gravimetric analysis (TG). When the MWCNT content and water-cement and MWCNTs/sodium dodecyl sulfonate (SDS) ratios were 0.45 wt%, 0.55, and 2.5:1, respectively, the carbonization depth and carbonization strength of the geopolymers were 69% and 176% of those the control group, respectively. The loss rate and relative dynamic elastic modulus after freeze-thaw were 28% and 121% of those of the control group, respectively. The Cl− diffusion depth and diffusion coefficient were 63% and 84% of those of the control group, respectively. Water-cement ratio affected the internal structure and crystallinity of geopolymer. MWCNTs mixed with SDS to modify geopolymers, the main function of MWCNTs was to densify the matrix and improve the internal cracks and pores. However, the excess SDS caused structural foaming and reduced the durability of the geopolymer.

The effects of multiwalled carbon nanotubes and Bacillus subtilis treatments on the salt tolerance of maize seedlings.

Nanomaterials, including multiwalled carbon nanotubes (MWCNTs), have been recently applied in agriculture to improve stress resistance, leading to contradictory findings for antioxidant responses and mineral nutrient uptake. A pot experiment involving maize in low-salinity sandy loam soils was conducted with the application of different concentrations (0, 20, 50 mg/L) of MWCNTs and the growth-promoting rhizobacterium Bacillus subtilis (B. subtilis). The dose-dependent effects of MWCNTs were confirmed: 20 mg/L MWCNTs significantly promoted the accumulation of osmolytes in maize, particularly K+ in the leaves and roots, increased the leaf indoleacetic acid content, decreased the leaf abscisic acid content; but the above-mentioned promoting effects decreased significantly in 50 mg/L MWCNTs-treated plants. We observed a synergistic effect of the combined application of MWCNTs and B. subtilis on plant salt tolerance. The increased lipid peroxidation and antioxidant-like proline, peroxidase (POD), and catalase (CAT) activities suggested that MWCNTs induced oxidative stress in maize growing in low-salinity soils. B. subtilis reduced the oxidative stress caused by MWCNTs, as indicated by a lower content of malondialdehyde (MDA). The MWCNTs significantly increased the leaf Na+ content and leaf Na+/K+ ratio; however, when applied in combination with B. subtilis, the leaf Na+/K+ ratio decreased sharply to 69% and 44%, respectively, compared to those of the control (CK) group, the contents of which were partially regulated by abscisic acid and nitrate, according to the results of the structural equation model (SEM). Overall, the increased osmolytes and well-regulated Na+/K+ balance and transport in plants after the combined application of MWCNTs and B. subtilis reveal great potential for their use in combating abiotic stress.

The Effect of Multi-Walled Carbon Nanotubes on the Compressive Strength of Cement Mortars

In this work, multi-walled carbon nanotubes (MWCNTs) have been synthesized using a modified method of solid-phase pyrolysis. The MWCNTs are effectively dispersed using a simple and facile method such as ultrasonic energy without and with surfactant for two different sonication times (15 min and 40 min). In the present study, the effect of MWCNT concentration (0.001, 0.01, 0.05, 0.1 wt.%) on the compressive strengths of cement mortars has been investigated. Compressive tests were carried out on an automatic pressure machine (C089) with a loading rate of 0.5 kN/s at the age of 7 days and 28 days. It is shown that the optimal value of the nanotubes’ concentration does not exist in the case of 15 min of sonication time, whereas the optimal value for 40 min of sonication time without and with surfactant is 0.01%. Moreover, in the absence of surfactants, the strength of the specimen over 7 days of hardening increased by 13%, and by 19.5% in the presence of surfactants. The compressive strength for a curing period of 28 days increased by 6.3% and 13.8%, respectively.

Modified carbon nanotubes/polyvinyl alcohol composite electrothermal films

Carbon nanomaterials are ideal materials for electrothermal applications because of their superior thermal conductivity, electrical conductivity, and mechanical properties. Electrothermal composites with excellent performance should have the characteristics of rapid temperature response, uniform heating temperature distribution, and good thermal stability after prolonged heating. However, for previously prepared electrothermal composites still have some shortcomings such as long temperature response time, uneven temperature distribution and poor thermal stability after long time heating. In this study, the composite electrothermal films with excellent performances were obtained by a layer-by-layer deposition approach, which were synthesized by pouring epigallocatechin gallate-functionalized multi-walled carbon nanotubes (E-MWCNTs) into a polytetrafluoroethylene mold and subsequently curing the polyvinyl alcohol (PVA) solution on the CNT layer. The electro-heating behavior of composite electrothermal film with different content and size was investigated by applying various voltages. They exhibit excellent electrothermal property, that is, a rapid temperature response, which can reach the steady-state temperature (TMAX) within 90 s. In addition, the maximum temperature can reach about 140 °C at 12 V. It was observed that the temperature of the composite electrothermal film has no significant change during the cycle tests of various voltages and 5 h aging time. According to the results of the experiment, the electrothermal properties of the composite electrothermal films are affected by the content of multi-walled carbon nanotubes (MWCNTs) and the applied voltage, which means that we can achieve accurate control of its properties by adjusting the content of MWCNTs and the applied voltage. Moreover, we have great expectations that these composite electrothermal films will have broad prospects for thermal management in wearable applications and electro-devices.

Strengthening the bonding interfaces of hybrid titanium carbon laminates by bionic micro texture and carbon nanotube pinning

A reliable strategy to enhance the bonding ability in hybrid titanium carbon laminates (HTCLs) is proposed, which is based on the pinning effect produced by bionic micro texture etched by laser on titanium and multi-walled carbon nanotubes (MWCNTs) introduced into adhesive layer. The characteristic of bionic micro texture is determined, and the strengthening mechanism of bonding interfaces is revealed. The HTCLs samples with various micro texture groove widths, laser scanning times and MWCNTs content are fabricated via an autoclave process. The micro texture morphologies, surface wettability, interlayer bonding properties under different conditions are studied. Results show that the recast layers formed on titanium during etching are beneficial to improve the interfacial bonding properties. Compared with no micro texture, the contact angle with micro texture can be reduced by 68.4%. Both micro texture and MWCNTs can reduce the defects at the interlayer interfaces and improve the interfacial adhesion. In this work, the maximum tensile shear strength (TSS) and interlaminar shear strength (ILSS) can be obtained with the micro texture groove width of 30 μm, the laser scanning of 30 times and the MWCNTs content of 0.4 wt%, which are 56.39% and 32.84% higher than that without any treatment, respectively.

Effect of Recycling on the Mechanical, Thermal and Rheological Properties of Polypropylene/Carbon Nanotube Composites

In this research the effect of physical recycling on the mechanical, thermal, and rheological properties of polypropylene (PP)/multiwalled carbon nanotube (MWCNT) was investigated. After melt homogenization by extrusion, specimens were injection moulded with 0.1 and 0.5 wt% MWCNT content. The recycling process was simulated by multiple grinding and re-moulding, then we compared the behavior of original and recycled PP/MWCNT composites. Differential scanning calorimetry (DSC) measurements proved that MWCNT had double the effect on the morphology of the PP matrix: on the one hand nucleating effect can be detected because 0.5 wt% MWCNT increased the onset temperature of crystallization by 10 °C, compared to the basic PP material; on the other hand, the crystalline fraction of the recycled composite materials decreased compared to the original PP material with the same MWCNT content. This resulted in a slight decrease in strength and stiffness but an increase in elongation at break. However, compared to the original unreinforced PP reference, even the recycled materials have better properties. The mechanical test results showed that recycled PP/MWCNT 0.5 wt% increased the elastic modulus (~15%) and decreased the tensile strain at yield (~10%). However, in the values of tensile stress at yield, relevant difference was not found. It was also shown by oscillatory rheometry that MWCNT had a significant effect on the rheological properties (storage and loss modulus, complex viscosity) of PP compounds in a wide temperature range (190-230 °C).

Thermal and exergy analysis of Pin-finned heatsinks for nanofluid cooled high concentrated photovoltaic thermal (HCPV/T) hybrid systems

• Cooling performance of HCPV/T is systematically investigated. • Different shaped pin-finned heat sinks (inline and staggered) are examined. • Thermal performance is determined for MWCNT nanofluids. • Exergy efficiencies of pin-fin heat sinks in HCPV/T are evaluated. • 2% MWCNT nanoparticle concentration is found to be the optimum. Cooling of High Concentrated Photovoltaic (HCPV) cells is a major concern among researchers due to higher heat generation in the cells from highly concentrated solar radiation. In the present investigation, a numerical study of the High Concentrated Photovoltaic Thermal (HCPV/T) system is conducted for the combined effect of nanofluids and pin-finned heatsinks on the cooling performance. The investigation is carried out for AZUR SPACE solar cell (Model: 3C44C) for 1000 Concentration Ratio (CR) and the Reynolds number ( Re ) varies within the laminar range (600 ≤ R e ≤ 2200). Different shapes of pin-fins and their orientations are systematically investigated for the effect of Multi-walled Carbon Nanotube (MWCNT) nanoparticles in a base fluid. The results show a significant reduction in the temperature (up to 18K) of the solar cells for the MWCNT nanofluid compared to its base fluid counterpart. A higher heat transfer characteristics (Nusselt numbers) and lower average temperature of top surface of HCPV cells are found to occur for the staggered arrangements of pin-fins. It is also noticed that the volume concentration of MWCNT in water affects heat transfer characteristics and reduction in temperature takes place up to the volume concentration of 2%. About 1.3% reduction in temperature is predicted for adding MWCNT nanoparticle concentration from 0.5% to 2%. However, in terms of exergy efficiency, maximum overall exergy (about 67% for water flow rate of 0.00167 kg/s) is found for square pin-fins with inline arrangements. The average increase in Nusselt number from inline to staggered arrangement are around 11%, 74%, and 22% respectively for circular, square and triangular fins. The maximum electrical efficiency reaches to 42.2% for both 2% and 4% MWCNT with staggered circular pin-fins for a mass flow rate of 0.0058kg/s. Finally, it appears that a combination of nanofluids and pin-finned heatsinks gives a better cooling rate in the HCPV/T system and could be a promising alternative along with other cooling techniques.

The effect of acid treated multi-walled carbon nanotubes on the properties of cement paste prepared by ultrasonication with polycarboxylate ester

Chemical functionalization of carbon nanotubes by the mix of sulfuric (H2SO4) and nitric (HNO3) acids has been reported to enhance the hydrophilicity of carbon nanotubes, which, in turn, improves its dispersion quality in aqueous solution and within the cement matrix. In this study, multi-walled carbon nanotubes (MWCNT) were treated by a mix of H2SO4 and HNO3, and used for preparation of MWCNT solutions by ultrasonic tip sonication with low amounts of polycarboxylate ester (PCE). The effects of acid functionalization on the dispersion of MWCNT, mechanical performance and hydration of cement paste were studied with respect to changes in MWCNT concentration, ultrasonication time and MWCNT:PCE ratio. According to the experimental results, acid-treated MWCNT contained 13 wt% of carboxyl functional group. The results from Raman spectroscopy showed the increased amount of unadsorbed PCE in solution with acid-treated MWCNT due to the increase in hydrophilicity. Increase in hydrophilicity contributed to a stronger bond between a-MWCNT and cement hydration products, and increased the mechanical strength of cement paste by 55%. The addition of a-MWCNT at 0.1 wt% concentration resulted in the increase of 28-day compressive strength from 40 MPa up to 62 MPa and flexural strength from 4.4 MPa up to 7.6 MPa. Retardation in hydration and increase in porosity were found to be associated with PCE that was not adsorbed on the surface of MWCNT.